The invention relates to stent deployment assemblies for use at a bifurcation and, more particularly, a catheter assembly for implanting one or more stents for repairing bifurcations, the aorto-ostium, and bifurcated blood vessels that are diseased, and a method and apparatus for delivery and implantation.
Stents conventionally repair blood vessels that are diseased and are generally hollow and cylindrical in shape and have terminal ends that are generally perpendicular to its longitudinal axis. In use, the conventional stent is positioned at the diseased area of a vessel and, after placement, the stent provides an unobstructed pathway for blood flow.
Repair of vessels that are diseased at a bifurcation is particularly challenging since the stent must overlay the entire diseased area at the bifurcation, yet not itself compromise blood flow. Therefore, the stent must, without compromising blood flow, overlay the entire circumference of the ostium to a diseased portion and extend to a point within and beyond the diseased portion. Where the stent does not overlay the entire circumference of the ostium to the diseased portion, the stent fails to completely repair the bifurcated vessel. Where the stent overlays the entire circumference of the ostium to the diseased portion, yet extends into the junction comprising the bifurcation, the diseased area is repaired, but blood flow may be compromised in other portions of the bifurcation. Unapposed stent elements may promote lumen compromise during neointimalization and healing, producing restenosis and requiring further procedures. Moreover, by extending into the junction comprising the bifurcation, the stent may block access to portions of the bifurcated vessel that require performance of further interventional procedures. Similar problems are encountered when vessels are diseased at their angled origin from the aorta as in the ostium of a right coronary or a vein graft. In this circumstance, a stent overlying the entire circumference of the ostium extends back into the aorta, creating problems, including those for repeat catheter access to the vessel involved in further interventional procedures.
Conventional stents are designed to repair areas of blood vessels that are removed from bifurcations and, since a conventional stent generally terminates at right angles to its longitudinal axis, the use of conventional stents in the region of a vessel bifurcation may result in blocking blood flow of a side branch or fail to repair the bifurcation to the fullest extent necessary. The conventional stent might be placed so that a portion of the stent extends into the pathway of blood flow to a side branch of the bifurcation or extend so far as to completely cover the path of blood flow in a side branch. The conventional stent might alternatively be placed proximal to, but not entirely overlaying the circumference of the ostium to the diseased portion. Such a position of the conventional stent results in a bifurcation that is not completely repaired. The only conceivable situation that the conventional stent, having right-angled terminal ends, could be placed where the entire circumference of the ostium is repaired without compromising blood flow, is where the bifurcation is formed of right angles. In such scenarios, extremely precise positioning of the conventional stent is required. This extremely precise positioning of the conventional stent may result with the right-angled terminal ends of the conventional stent overlying the entire circumference of the ostium to the diseased portion without extending into a side branch, thereby completely repairing the right-angled bifurcation.
To circumvent or overcome the problems and limitations associated with conventional stents in the context of repairing diseased bifurcated vessels, a stent that consistently overlays the entire circumference of the ostium to a diseased portion, yet does not extend into the junction comprising the bifurcation, maybe employed. Such a stent would have the advantage of completely repairing the vessel at the bifurcation without obstructing blood flow in other portions of the bifurcation. In addition, such a stent would allow access to all portions of the bifurcated vessel should further interventional treatment be necessary. In a situation involving disease in the origin of an angulated aorto-ostial vessel, such a stent would have the advantage of completely repairing the vessel origin without protruding into the aorta or complicating repeat access.
In addition to the problems encountered by using the prior art stents to treat bifurcations, the delivery platform for implanting such stents has presented numerous problems. For example, a conventional stent is implanted in the main vessel so that a portion of the stent is across the side branch, so that stenting of the side branch must occur through the main-vessel stent struts. In this method, commonly referred to in the art as the xe2x80x9cmonoclonal antibodyxe2x80x9d approach, the main-vessel stent struts must be spread apart to form an opening to the side-branch vessel and then a catheter with a stent is delivered through the opening. The cell to be spread apart must be randomly and blindly selected by recrossing the deployed stent with a wire. The drawback with this approach is there is no way to determine or guarantee that the main-vessel stent struts are properly oriented with respect to the side branch or that the appropriate cell has been selected by the wire for dilatation. The aperture created often does not provide a clear opening and creates a major distortion in the surrounding stent struts. The drawback with this approach is that there is no way to tell if the main-vessel stent struts have been properly oriented and spread apart to provide a clear opening for stenting the side-branch vessel.
Another approach to providing a main-vessel stent that does not block access to the ostium of a side-branch vessel is to cut an aperture in the side-wall of the main-vessel stent. The draw-back to this approach is that forming the aperture in this manner interferes with the structural integrity of the stent in the area of the aperture, resulting in reduced strength and scaffolding. Additionally, where such an aperture is cut into a stent having otherwise closed cells formed from stent struts, the perimeter of the aperture will have open cells and unjoined stent struts presenting a jagged perimeter that may interfere with crossing of the aperture by a guide wire or catheter if subsequent treatment of the side-vessel is required.
In another prior art method for treating bifurcated vessels, commonly referred to as the xe2x80x9cCulotte technique,xe2x80x9d the side-branch vessel is first stented so that the stent protrudes into the main vessel. A dilatation is then performed in the main vessel to open and stretch the stent struts extending across the lumen from the side-branch vessel. Thereafter, the main-vessel stent is implanted so that its proximal end overlaps with the side-branch vessel. One of the drawbacks of this approach is that the orientation of the stent elements protruding from the side-branch vessel into the main vessel is completely random. Furthermore the deployed stent must be recrossed with a wire blindly and arbitrarily selecting a particular stent cell. When dilating the main vessel stretching the stent struts is therefore random, leaving the possibility of restricted access, incomplete lumen dilatation, and major stent distortion.
In another prior art device and method of implanting stents, a xe2x80x9cTxe2x80x9d stent procedure includes implanting a stent in the side-branch ostium of the bifurcation followed by stenting the main vessel across the side-branch ostium. In another prior art procedure, known as xe2x80x9ckissingxe2x80x9d stents, a stent is implanted in the main vessel with a side-branch stent partially extending into the main vessel creating a double-barreled lumen of the two stents in the main vessel distal to the bifurcation. Another prior art approach includes a so-called xe2x80x9ctrouser legs and seatxe2x80x9d approach, which includes implanting three stents, one stent in the side-branch vessel, a second stent in a distal portion of the main vessel, and a third stent, or a proximal stent, in the main vessel just proximal to the bifurcation.
All of the foregoing stent deployment assemblies suffer from the same problems and limitations. Typically, there is uncovered intimal surface segments on the main vessel and side-branch vessels between the stented segments. An uncovered flap or fold in the intima or plaque will invite a xe2x80x9csnowplowxe2x80x9d effect, representing a substantial risk for subacute thrombosis, and the increased risk of the development of restenosis. Further, where portions of the stent are left unapposed within the lumen, the risk for subacute thrombosis or the development of restenosis again is increased. The prior art stents and delivery assemblies for treating bifurcations are difficult to use, making successful placement nearly impossible. Further, even where placement has been successful, the side-branch vessel can be xe2x80x9cjailedxe2x80x9d or covered so that there is impaired access to the stented area for subsequent intervention. The present invention solves these and other problems as will be shown.
In addition to problems encountered in treating disease involving bifurcations for vessel origins, difficulty is also encountered in treating disease confined to a vessel segment but extending very close to a distal branch point or bifurcation which is not diseased and does not require treatment. In such circumstances, very precise placement of a stent covering the distal segment, but not extending into the ostium of the distal side-branch, may be difficult or impossible. The present invention also offers a solution to this problem.
References to distal and proximal herein shall mean: the proximal direction is moving away from or out of the patient and distal is moving toward or into the patient. These definitions will apply with reference to body lumens and apparatus, such as catheters, guide wires, and stents.
The invention provides for improved stent designs and stent delivery assemblies for repairing a main vessel and side-branch vessel forming a bifurcation, without compromising blood flow in other portions of the bifurcation, thereby allowing access to all portions of the bifurcated vessels should further interventional treatment be necessary. The stent delivery assemblies of the invention all share the novel feature of containing, in addition to a tracking guide wire, a second positioning wire which affects rotation and precise positioning of the assembly for deployment of the stent.
A stent is provided for implanting in the main vessel adjacent to a bifurcation in which a cylindrical member has distal and proximal ends and an outer wall surface therebetween, which can typically be similar to the outer wall surface of stents used in the coronary arteries. An aperture is formed in the outer wall surface of the apertured stent and is sized and positioned on the outer wall surface so that when the apertured stent is implanted in the main vessel, the aperture is aligned with the side-branch vessel providing unrestricted blood flow from the main vessel through to the side-branch vessel. Deployment of the apertured stent is accomplished by a novel stent delivery system adapted specifically for treating bifurcated vessels.
The aperture is formed in the outer wall of the stent by configuring the undulating or serpentine pattern of the cylindrical elements of the stent to provide the aperture. Reconfiguring the pattern in this manner provides an aperture perimeter formed of closed stent cells. This construction provides increased strength in the area of the aperture as well as improved scaffolding of the vessel wall surrounding the ostium.
In general, the aperture is formed in the stent by adjusting the pattern of stent cells and stent struts so that the size of the stent cell in the region of the stent surrounding the aperture is less than the stent cells in the remainder of the stent. Preferably, the stent cells in the region including the aperture are half the size of remaining stent cells. The smaller cell size in the region of the aperture results in an aperture perimeter that is smaller and denser, providing both increased scaffolding of the vessel wall surrounding the ostium of a side-branch vessel as well as providing a smoother lumen for accessing the side-branch vessel should subsequent treatment of the side-branch vessel be necessary.
The stent delivery system of the present invention further includes a main-vessel catheter for delivering a stent in the main vessel after the side-branch vessel has been stented. The main-vessel catheter includes a tracking guide wire lumen extending through at least a portion thereof, and adapted for receiving a tracking guide wire for slidable movement therein. An expandable member is positioned near the main-vessel catheter distal end for delivering and implanting a main-vessel (apertured) stent in the main vessel. The main-vessel stent includes an aperture on its outer surface which aligns with the side-branch vessel. A positioning guide wire lumen is associated with the expandable member, and is sized for slidably receiving the stent-positioning guide wire. The stent-positioning guide wire slides within the positioning guide wire lumen to orient the expandable member so that it is positioned adjacent to, but not in, the side-branch vessel with the stent aperture facing the side-branch ostium.
In one embodiment, the main-vessel catheter assembly includes the so-called rapid exchange catheter features which are easily exchangeable for other catheters while the tracking and positioning guide wires remain positioned in the side-branch vessel and the main vessel, respectively. In an alternate embodiment, both catheters may be of the xe2x80x9cover-the-wirexe2x80x9d type.
The present invention further includes a method for delivering the main-vessel (apertured) stent in the bifurcated vessel.
In the event that the main vessel is to be stented (with the stent placed across the bifurcation site), the proximal end of the main-vessel guide wire is inserted into the distal end of the guide wire lumen of the main-vessel catheter. The main-vessel catheter would then be advanced into the body until the catheter is within one cm or so of the target site. The distal end of the second (integrated, stent-positioning) guide wire, which resides in the main-vessel catheter during delivery to the main vessel, is then advanced by having the physician push the positioning wire from outside the body. The distal end of the stent-positioning wire travels through the positioning guide wire lumen and passes underneath the proximal half of the stent until it exits at the site of the stent aperture. The catheter is then advanced distally until resistance is felt from the stent-positioning guide wire pushing up against the ostium of the side-branch vessel indicating that the stent aperture is correctly facing the side-branch vessel ostium. If a stent has already been implanted in the side-branch vessel, this resistance also ensures that the aperture of the main vessel stent is aligned with the proximal end of the side-branch stent. Thereafter, the expandable member on the main-vessel catheter is inflated, thereby expanding and implanting the main-vessel stent into contact with the main vessel, with the aperture in the stent providing a flow path for the blood from the main vessel through to the side-branch vessel without any obstructions. The expandable member is deflated and the main-vessel catheter is removed from the body. The main-vessel catheter is designed so that both the main-vessel guide wire and side-branch wire can be left in their respective vessels should sequential or simultaneous high pressure balloon inflation be required in each of the vessels in order to complete the stenting procedure. The presence of the stent-positioning wire in the stent aperture permits catheter access through this aperture into the side-branch vessel for balloon inflation to smooth out the aperture in the main-vessel stent. This additional step is a matter of physician choice.
Utilizing this method, the main vessel can be stented without the need for stenting the side-branch vessel. An advantage of this embodiment is that a major side branch, not diseased and requiring treatment, exiting from a main vessel requiring stenting, may be protected by the positioning wire while the main vessel is stented. If xe2x80x9csnowplowingxe2x80x9d compromise or closure of the side-branch vessel occurs with main-vessel stenting, then access is already present and guaranteed for stenting of the side-branch vessel over the wire already in place in the manner described above. This will allow confident stenting of a main vessel segment containing a major side branch. In this usage, only if compromise or occlusion of the side branch occurs, will additional stenting of the side branch be required.
In an alternative embodiment, the stent to be implanted in the main-vessel is mounted on a main-vessel catheter having an expandable section including two expandable balloons closely spaced together but separated sufficiently so that an exit port formed in the wall of the main-vessel catheter is exposed, allowing a stent-positioning guidewire to exit the catheter. In normal use, the stent is mounted such that the aperture of the stent is aligned with the exit port, allowing the stent-positioning guidewire to extend out of the exit port and through the stent. In this embodiment, the main-vessel catheter is advanced into the body until the catheter is within one cm or so of the target site. The distal end of the stent-positioning guide wire, which resides in the main-vessel catheter during delivery to the main vessel, is then advanced by having the physician push the positioning wire from outside the body. The distal end of the stent-positioning wire travels through the positioning guide wire lumen until it exits through the exit port between the balloons at the site of the stent aperture. The catheter is then advanced distally until resistance is felt from the stent-positioning guide wire pushing up against the ostium of the side-branch vessel indicating that the stent aperture is correctly facing the side-branch vessel ostium. The remainder of the method is as described above. The main-vessel catheter is designed so that both the main-vessel guide wire and side-branch wire can be left in their respective vessels should sequential or simultaneous high pressure balloon inflation be required in each of the vessels in order to complete the stenting procedure. A further advantage of this method is that both the main-vessel guide wire and side-branch wires are contained within the catheter body, allowing for use of either an integrated main-vessel/side-branch guide wire system or simply running two separate guide-wires through a central lumen of the catheter. Alternatively, the main-vessel catheter may include two separate lumens to accommodate the main-vessel and side-branch guide wires.
Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.